By Jonathan Moreland, founder of Insider Insights and author of Profit From Legal Insider Trading.

NEW YORK ( TheStreet) -- It is a victory for common sense. Tracking the trading behavior of company executives, directors and large shareholders in the stocks of firms they're registered in as "insiders" has proven to be profitable, according to both academic studies and (more importantly) the experience of professional investors.

Below are lists of the top 10 mainly open-market insider purchases and sales filed at the Securities and Exchange Commission Tuesday, May 21, 2013 as ranked by dollar value. Please note, however, that these are only factual lists, not buy and sell recommendations. Dollar value is only one metric to assess the importance of an insider transaction, and, frankly, often not even the most important metric that determines if an insider transaction is significant.

At, we find new investment ideas just about every day using these and more intricate insider screens to determine where we should focus our subsequent fundamental and technical analysis. And while stocks don't (or shouldn't) move up or down based on insider activity alone, insiders tend to be good indicators of when real stock-moving events like earnings surprises, corporate actions, and new products may be in the offing.

So use these regular Top Insider Trades columns as the initial research tools they are meant to be, and click the links in the tables to analyze a company's or insider's full insider history. Also feel free to contact us with any questions on our proprietary insider data, and how it is best analyzed.
Chesapeake (CHK) Dunham A DIR 450,000 9,401,895
Spectrum (SPB) Harbinger BO 101,199 5,972,019
Ambit (AMBI) Marchington A DIR 431,527 3,452,216
Silver Bay (SBY) Kessler I R DIR 54,623 985,399
Apache (APA) Farris G S CB,CEO,DIR 10,000 836,908
Customers Banc (CUBI) Way T L DIR 24,628 412,519
Opko (OPK) Frost P CEO,CB,BO 54,400 384,811
Griffon (GFF) Mehmel R F PR,COO 30,000 350,707
Lionbridge (LIOX) Glenhill BO 125,396 347,366
Vocus (VOCS) Burns K J DIR 25,000 212,500
Source: Insider Insights
Nielsen (NLSN) Valcon BO 40,238,476 1,387,619,840
Nielsen (NLSN) Kkr BO 8,313,661 286,695,776
Symetra (SYA) Levy S M DIR 6,089,999 81,803,912 (WWWW) General BO 2,000,000 42,860,000
Huntsman (HUN) Huntsman J M CB,DIR,BO 952,769 18,885,806
Reynolds (RAI) Brown & Williamson BO 225,546 11,074,309
Epl (EPL) Wexford O 304,418 10,040,279
YELP (YELP) Deer Vi DIR,BO 289,707 9,078,912
Marsh & McLennan (MMC) Moczarski A PR,CEO 173,216 7,066,434
Equity One (EQY) Hetz Nathan O 127,162 3,298,315
Source: Insider Insights

Key to Titles: A=Assistant, AI=Affiliated Investor, AO=Accounting Officer, BD=Business Development, BO=Beneficial Owner, CAO=Chief Accounting Officer, CB=Chairman, CCO=Chief Compliance Officer, CEO=Chief Executive Officer, CFO=Chief Financial Officer, CIO=Chief Information Officer, CO=Compliance Officer, COO=Chief Operating Officer, CT=Controller, CTO=Chief Technology Officer, DIR=Director, EVP=Executive Vice President, F=Founder, FO=Financial Officer, GC=General Counsel, HR=Human Resources, IO=Information Officer, IR=Investor Relations, LO=Legal Officer, MD=Managing Director, O=Officer, OO=Operating Officer, PR=President, PT=Partner, REL=Relative of an insider, SEC=Secretary, SH=Shareholder, SO=Sales Officer, TO=Technology Officer, TR=Treasurer, TT=Trustee, VCB=Vice Chairman, VP=Vice President, X=Ex Officer or other title displayed.

Jonathan Moreland is the founder of, which produces a weekly newsletter and offers professional screening and alerting tools to analyze a proprietary, real-time insider data feed. He is also the principal of Insider Asset Management, a registered investment advisor in New York. Mr. Moreland has been analyzing insider data professionally for two decades and has been a contributor to since 2001. A fundamental analyst with an MBA in finance, Mr. Moreland long ago identified insider data as an excellent first screen to determine where to focus his research efforts. He is quoted frequently in the media for his insider analysis and stock recommendations stemming from it. He is also author of Profit From Legal Insider Trading.

Under no circumstances does the information in this column represent a recommendation to buy or sell stocks. While he cannot provide investment advice or recommendations, Moreland appreciates your feedback; click here to send him an email.